E08
Keston
Air Pressure Switch / Flue Differential Fault
Boiler displays E08 and will not start, fan may not run
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blocked flue, Condensate trap full, Split or blocked pressure tubing, Faulty air pressure switch
How to Fix / Troubleshooting
Safety: Do not attempt to run the boiler with a suspected flue fault. Isolate power and gas.
User checks:
- Check outside that the Keston flue terminal is clear of obstructions.
- Ensure the condensate discharge pipe is not frozen or kinked.
Engineer checks:
- Remove and clean the condensate trap and check the internal flue connections for water or debris.
- Inspect the silicone tubes from the fan to the air pressure switch for splits, blockages, or incorrect routing; replace if necessary.
- Test the air pressure switch with a manometer or by applying gentle pressure/vacuum and checking contact changeover with a multimeter.
- Verify correct flue installation and length as per Keston installation manual; rectify any non-compliant runs or joints.
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Repair Difficulty
Hard
4/5
Required Part
Air Pressure Switch
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